1. Field of Invention
The present disclosure relates to a control technology of three-phase grid equipment. More particularly, the present disclosure relates to a control device of a power conversion unit and a method of controlling a power conversion unit.
2. Description of Related Art
Nowadays, with the development of technology and great enrichment of material life of human beings, the accompanying energy problems and environmental problems are becoming more and more serious. As a result, the development and utilization of renewable energy to solve the above-mentioned problems have become a critical direction of research and development, for example, wind power having the features of cleanliness and environmental friendliness is well deserved to be one of many types of renewable energy sources.
The common grid equipment includes the grid inverter for wind power and photovoltaic power, the reactive compensation device, the motor inverter for driving the motor, etc. When the three-phase voltage signal of the three-phase AC grid sags symmetrically in a short time, the above grid-connected equipment should remain not tripping and be able to quickly generate reactive currents to support the three-phase grid voltages so as to reduce the impact of grid voltage fault. However, when the three-phase voltage signal of the three-phase AC grid is asymmetrically faulty at a high voltage value, voltages of specific phases will be lower than a normal value and a voltage of a specific phase will be higher than the normal value. Under the circumstances, if the above equipment simply generates the reactive currents to support the three-phase grid voltages, the higher phase voltage will become even higher, which in turn leads to shutdown of the above-mentioned grid equipment due to a fault. Take the grid inverter for example, the magnitude of the DC busbar voltage of the grid inverter determines the peak value of the maximum inverted AC voltage, the phase grid voltage signal having an over high value will deteriorate its ability of controlling the grid current, thus saturating the modulation wave or even causing uncontrollable circumstances to happen.
For the forgoing reason, there is a need for solving the above-mentioned problem by providing a control device of a power conversion unit and a method of controlling a power conversion unit.